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Lawrence SnyderUniversity of Washington, Seattle
© Lawrence Snyder 2004
Connected computers are better! How’s it done?
Computers are useful alone, but are better when connected (networked) Access more information and software
than is stored locally Help users to communicate, exchange
information…changing ideas about social interaction
Perform other services—printing, Web, email, texting, mobile, etc.
Today’s Message: Internet is NOT really a bunch of tubes!Today’s Message: Internet is NOT really a bunch of tubes!
04/21/23 2© 2011-2014 Larry Snyder, CSE
Networks are structured differently based (mostly) on distance between computers: Local area network (LAN)
▪ Small area: room or building▪ Either wired (Cu or fiber) or wireless
Wide area networks (WAN)▪ Large area: more than 1 km▪ Fiber-optic, copper transmission lines, μ-wave,
satellite Metropolitan area networks (MAN)
▪ Neighborhood or several blocks of business district▪ Private service provider owns network
04/21/23 3© 2011-2014 Larry Snyder, CSE
To communicate computers need to know how to set up the info to be sent and interpret the info received Communication rules are a protocol Example protocols
▪ EtherNet—for physical connection in a LAN ▪ TCP/IP—for Internet—transmission control
protocol / internet protocol▪ HTTP—for Web—hypertext transfer protocol
04/21/23 4© 2011-2014 Larry Snyder, CSE
EtherNet is a popular LAN protocol▪ It uses a “party” protocol
Connection to campus network infrastructure
PC PC PC PC PC PCEther Net Cable
Typical MGH or OUGL Lab
04/21/23 5© 2011-2014 Larry Snyder, CSE
The campus subnetworks interconnect computers of the UW domain which connects to Internet via a gateway
All communication by TCP/IP All communication by TCP/IP
Homer
Dante
Student CS
ODGGateway
Switch
Switch
washington.edu
04/21/23 6© 2011-2014 Larry Snyder, CSE
Information is sent across the Internet using IP—Cerf uses postcard analogy
▪ Break message into fixed size units▪ Form IP packets with destination address,
sequence number and content▪ Each makes its way separately to
destination, possibly taking different routes▪ Reassembled at destination forming msgKey Point: Taking separate routes lets
packets by-pass congestion and out-of-service switches; packet reassembly discovers lost packets; ask for resend
Key Point: Taking separate routes lets packets by-pass congestion and out-of-service switches; packet reassembly discovers lost packets; ask for resend
addr # data
04/21/23 7© 2011-2014 Larry Snyder, CSE
04/21/23 © 2011-2014 Larry Snyder, CSE 8
04/21/23 9© 2011-2014 Larry Snyder, CSE
04/21/23 10© 2011-2014 Larry Snyder, CSE
whatismyipaddress.com/traceroute-toolwhatismyipaddress.com/traceroute-tool
IP-addresses
As with “wired Ethernet,” all computers in range can hear the radio signals of the others
04/21/23 © 2011-2014 Larry Snyder, CSE 11
People name computers by a domain name a hierarchical scheme that groups like
computers▪ .edu All educational computers, a TLD▪ .washington.edu All computers at UW▪ dante.washington.edu A UW computer▪ .ischool.washington.edu iSchool computers▪ .cs.washington.edu CSE computers▪ spiff.cs.washington.edu A CSE computerPeers
Domains begin with a “dot” and get “larger” going rightDomains begin with a “dot” and get “larger” going right
04/21/23 12© 2011-2014 Larry Snyder, CSE
Computers are named by IP address, four numbers in the range 0-255
cse.washington.edu: 128.95.1.4ischool.washington.edu: 128.208.100.150
Remembering IP addresses would be brutal for humans, so we use domains
Computers find the IP address for a domain name from the Domain Name System—an IP address-book computer
A computer needs to know IP address of DNS server!A computer needs to know IP address of DNS server!04/21/23 13© 2011-2014 Larry Snyder, CSE
.edu .com .mil .gov .org .net domains are “top level domains” for the US Recently, new TLD names added Each country has a top level domain name:
▪ .ca (Canada)▪ .es (Spain)▪ .de (Germany)▪ .au (Australia) ▪ .at (Austria)▪ .us (US)
Do you know sites like:bit.lywww.nba.tvdel.icio.us… they exploit TLDs
Do you know sites like:bit.lywww.nba.tvdel.icio.us… they exploit TLDs
04/21/23 14© 2011-2014 Larry Snyder, CSE
View the Internet in two ways:1. Humans see a hierarchy of domains
relating computers—logical network 2. Computers see groups of four number IP
addresses—physical network (my computer: 128.208.3.136 )
Both are ideal for the “user's” needsThe Domain Name System (DNS)
relates the logical network to the physical network by translating domains to IP addresses
04/21/23 15© 2011-2014 Larry Snyder, CSE
Many people mis-use the terms “Internet” and “World Wide Web”
Let’s get them right
Internet: all of the wires, fibers, switches, routers etc. connecting named computers
Internet: all of the wires, fibers, switches, routers etc. connecting named computers
Web: That part of the Internet —web servers—that store info and serve Web pages and provide other services to client computers
Web: That part of the Internet —web servers—that store info and serve Web pages and provide other services to client computers
04/21/23 16© 2011-2014 Larry Snyder, CSE
The Web and much of the Internet services use the client server form of interaction
It’s a VERY BRIEF relationship04/21/23 © 2011-2014 Larry Snyder, CSE 17
Clients and servers are not connected – they only exchange info … “no commitment issues”
04/21/23 © 2011-2014 Larry Snyder, CSE 18
Networking changed the worldInternet: named computers using TCP/IPWWW: servers providing Web pages Principles
▪ Logical network of domain names▪ Physical network of IP addresses▪ Protocols rule: LAN, TCP/IP, http...▪ Domain Name System connects the two▪ Client/Server, fleeting relationship on WWW
04/21/23 19© 2011-2014 Larry Snyder, CSE
Pair programming – two people work side-by-side programming one problem together It’s thought to be more productive – fewer
errors, smarter code It’s certainly more fun
CSE120 Rules – ALL CODING WORK ON PROJECT MUST BE
DONE TOGETHER Share coding duties, commenting duties
Teams: comparable skill, compatible times
04/21/23 © 2011-2014 Larry Snyder, CSE 20
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